clematis and hydrangea

(Question)

Hi
I have clematis stem reached like 12 feet. This year, so far, it look dead. The other stems changed to green or maybe new one took over so I can not tell. My question, should I cut the stem of the clematis in fall or other time or leave it as it is. Because I was hoping this year, the clematis will be even higher. The same question I have for the hydrangea. should I keep the stems or cut them after the bloom finish? thank you

(Answer)

Thank you for contacting the Toronto Master Gardeners with your inquiry about the timing of pruning of hydrangeas and clematis.

As a general principal it is important to understand when certain shrubs or vines set their flower buds, and whether they b;loom from old wood or new wood. Generally , shrubs or vines that set their buds in the previous summer or fall, will bloom on this old wood or stems earlier the next year. Then there are those shrubs or vines that flower from the new growth that emerge in the new year and bloom later in the season. The specifics of how you prune Clematis and Hydrangea follows these general principals, but I will spell out the details.

Hydrangeas;

To determine if your hydrangea blooms on old wood, think about when it flowers. Shrubs with this characteristic generally begin blooming in early summer and peter out by midsummer, though sporadic blooms may appear afterward. These shrubs form next year’s flower buds in late summer or early fall as the days get shorter and temperatures cool off. To reduce the risk of removing these buds, prune just as the flowers begin to fade. Often, the earlier you get it done after bloom, the quicker the shrub can recover, producing more and larger blooms next season.

Clematis;

Clematis are classified into three pruning type which determine when to prune them.

Group 1 vines flower in spring, on growth from the previous year.

Prune these vines right after they finish blooming in spring. The new stems that grow will then have enough time to make flower buds for the following year.

Group 2 vines bloom in late spring or early summer, then again sporadically, on new shoots and old stems.

A few approaches are effective when pruning this group. The most refined approach is to lightly thin out and disentangle stems before growth begins in late winter or early spring, and then go over the plant again after the earliest flowers fade in late spring or early summer, severely shortening the stems that bore those flowers. If the plant tends to bloom more heavily later rather than earlier in the season, you can be more heavy-handed when thinning stems before growth begins in early spring.

A simpler option when pruning Group 2 clematis vines is to severely prune the plant back by half in alternate years. Another approach is to cut the whole plant back drastically every few years just before growth begins, with little or no pruning in the intervening time; in this case, you give up only the earliest blossoms in the season you prune.

Group 3 vines flower in late summer or in fall, on new growth produced earlier in the season.

These are the easiest vines to prune. Just before the season’s growth begins, or as it is beginning, lop all stems back to strong buds within a foot or so of the ground. If you prefer to let these types continue to grow year after year , it is ok to let them just continue without being pruned.